/Engine/Source/Runtime/SlateCore/Public/Rendering/DrawElementTypes.h
Creates a custom element which can be used to manually draw into the Slate render target with graphics API calls rather than Slate elements
static void MakeCustom ( [FSlateWindowElementList](API\Runtime\SlateCore\Rendering\FSlateWindowElementList) & ElementList, uint32 InLayer, [TSharedPtr](API\Runtime\Core\Templates\TSharedPtr)< [ICustomSlateElement](API\Runtime\SlateCore\Rendering\ICustomSlateElement), ESPMode::ThreadSafe > CustomDrawer )